Gabriela is 12 years older than Tiffany. Twelve years ago, Gabriela was 5 times as old as Tiffany. How old is Tiffany now?
Answer: We can use the given information to write down two equations that describe the ages of Gabriela and Tiffany. Let Gabriela's current age be $g$ and Tiffany's current age be $t$ The information in the first sentence can be expressed in the following equation: $g = t + 12$ Twelve years ago, Gabriela was $g - 12$ years old, and Tiffany was $t - 12$ years old. The information in the second sentence can be expressed in the following equation: $g - 12 = 5(t - 12)$ Now we have two independent equations, and we can solve for our two unknowns. Because we are looking for $t$ , it might be easiest to use our first equation for $g$ and substitute it into our second equation. Our first equation is: $g = t + 12$ . Substituting this into our second equation, we get the equation: $(t + 12)$ $-$ $12 = 5(t - 12)$ which combines the information about $t$ from both of our original equations. Simplifying both sides of this equation, we get: $t + 0 = 5 t - 60$ Solving for $t$ , we get: $4 t = 60$ $t = 15$.